Cholesterol and Cholesterol Oxides on
Coronary Heart Diseases
Trends in egg consumption in U.S. and
the reason
A. Egg Consumption:
- 403 in 1945
- 234 in 1993 (176 Table eggs, 58 Processed eggs)
- 256 in 2004
B. Major concerns: Cholesterol and Fat in eggs
- Cholesterol in egg: 213 mg/large egg (1989)
30% of Yolk
- Cholesterol in meat: 70-80 mg/100 g
How Cholesterol is Used in the Animal
Body
21
CH3
22
26
24
CH3
20
18
CH3
12
19
CH3
16
27
CH3
14
15
9
1
10
2
8
5
3
25
17
13
11
23
4
OH
Vitamin D
7
6
Cholesterol
Cell Membrane
Hormones Bile
Skin
Cholesterol and CHD: Theories
- Plasma lipid theory
- Response-to-Injury hypothesis: Lipid and
cholesterol oxidation products cause injury
- Combined “Lipid” and “Injury” Hypothesis
Arteriosclerosis and CHD
„
„
Atherosclerosis: general term for a condition
characterized by thickening, hardening, and
loss of elasticity of the walls of the blood
vessels.
CHD: condition that results when the coronary
arteries are narrowed or occluded, most
commonly by atherosclerotic deposits of
fibrous and fatty tissue. Coronary artery
disease is the most common underlying cause
of cardiovascular disability and death.
Plasma lipid theory (Infiltration theory)
„
The infiltration of LDL cholesterol into the
wall of an artery is the major factor in the
infiltration and progression of
atherosclerotic plaques.
„
Cholesterol plays a pivotal role.
Plasma lipid theory (Infiltration theory)
- Anitschew (1913): High frequency atherosclerosis in
rabbits when fed cholesterol
- Feeding 2% cholesterol diet increased serum
cholesterol level by 90 folds and increased
atherosclerotic lesion (Langner and Bement, 1985).
- Epidemiological Studies: High serum Cholesterol is
related to atherosclerosis
- Intervention reduced atherosclerosis: Cholestryamine
(increase the rate of bile excretion)
- High cholesterol induced atherosclerosis but the
response varied among rabbits (Duff et al., 1957)
- LDL receptor theory of Goldstein and Brown (1976):
familial hypercholesterolemia
Does dietary cholesterol raise serum
cholesterol?
- At very high level of intake (> 1000 mg per day):
yes. Because physiological compensation
mechanisms (decreased synthesis and
absorption of Cholesterol increased excretion via
bile salts) are not good enough to maintain SC
level
- At 500 - 800 mg level: 70% can maintain
homeostasis by the compensation mechanisms.
Approximately 30% increased Sc level
temporarily and went back to normal.
- Only U.S. has dietary cholesterol level in a dietary
guideline
Response-to-Injury Hypothesis
- An injury to the endothelium is the initiating
event in atherogenesis
- Reinterpretation of cholesterol study
Questions on the purity of cholesterol (Taylor
et al., 1979)
- USP grade cholesterol was contaminated with
cholesterol oxidation products (COPS)
- Epidemiological study: Indian immigrants to
London
Biological effects of cholesterol
oxides
- Atherogenicity
- Angiotoxicity
- Cytotoxicity
- Mutagenecity
- Inhibition of enzyme activities:
HMGCoAR
Cholesterol Oxides
7α-OH or 7β-OH cholesterol
5,6α- or 5,6β-epoxides
Cholestanetriol
7-keto cholesterol
5 α-hydroperoxycholesterol
Endothelial cell injury: Mechanically
and chemically
- Hypertension
- Plasma LDL: familial and diet related
- Toxins: COPS, virus, and drugs
- Pure cholesterol was not atherogenic nor
angiotoxic in spite of being able to induce
hypercholesterolemia
- Each COPS were angiotoxic and atherogenic:
Cholestan triol, 25-hydroxycholesterol are the
most potent atherogenic agents
Combined “Lipid” and “Injury” Hypothesis
- Endothelial injury by Lipid Oxidation Products and
then plaque accumulation by LDL-cholesterol
- COPS are initiators of atherosclerosis
- Cholesterol is involved in plaque deposition
- Cholesterol deposition is merely a secondary
process preceded by a complex series of
pathological changes involving the interplay of
endothelial cells, macrophages, platelets, growth
factors, chemotactic factors, lipoproteins, and
foam cells.
Angiotoxicity and cytotoxicity
- Explain their role as initiators of
atherosclerotic lesions
- Endothelial cell damage initiates the
complex series of pathological changes
leading ultimately to plaque, wall
thickening, and lumen narrowing
Atherosclerotic cascade
• Wound by toxin or hypertension (right
brachiocephalic artery is more susceptible)
• Release of chemokines, accumulation of
platelets for healing
• Monocytes cross the endothelial cell layer and
scavenge oxidized LDL
• Foam cell formation and then fatty streak
• Foam cells secrete chemokines, and platelets
and foam cells secrete growth factors
Atherosclerotic cascade
• More monocytes/macrophages and Tlymphocytes accumulate
• Swelling and damage of endothelial cells by the
free radicals and smooth cell growth
• Cell rupture and platelets aggregation as a
process of wound healing
• LDL, cholesterol esters, lipid, collagen, calcium
deposition
• Plaque formation
• Obstruct arteries and thrombosis
Cholesterol Oxidation
- In solid phase (crystalline cholesterol): side chain
oxidation
- In aqueous solution: autoxidation similar to that of
other lipids
- Exposure to air, heat, light and radiation accelerate
cholesterol oxidation
- Variety of COPS are found in foods: milk products,
egg products, fish products
- COPS are absorbed in intestine and transferred by
LDL and VLDL
Types of heat treatment on oxysterols
formation in spray-dried egg mix
--------------------------------------------------------------------------------------------------------------------------------------------------
Oxysterol
Indirect heat
(mg/g)
Direct heat
(mg/g)
Increase
(%)
--------------------------------------------------------------------------------------------------------------------------------------------------
7α-hydroxy cholesterol
7β-hydroxy cholesterol
α-epoxide
β-epoxide
25-hydroxy cholesterol
7-ketocholesterol
Cholestantriol
1.8
1.5
21.5
1.9
1.4
2.0
11.6
7.0
18.5
50.0
37.4
5.1
37.0
13.0
289
1133
132
1868
264
1750
12
--------------------------------------------------------------------------------------------------------------------------------------------------
Missler et al. (1985, J. Food Sci. 50: 229)
Oxysterols (ppm/food sample) in processed
meats
-------------------------------------------------------------------------------------------------------------------------------------------------
Processed Meat
25-OH
7 α-OH
7 β-OH
triol
-------------------------------------------------------------------------------------------------------------------------------------------------
Cooked Bratwrust
Beef Franks
Chicken rolls
Cooked Hamburgers
Cooked lean bacon
Raw hamburger
Turkey bologna
Tr
Tr
Tr
Tr
Tr
Tr
Tr
820.0
98.5
Tr
72.0
Tr
Tr
NA
Tr
34.0
Tr
NA
NA
36.0
NA
1335.0
Tr
Tr
NA
Tr
1298.0
86.0
-------------------------------------------------------------------------------------------------------------------------------------------------
Higley et al. (1986, Meat Sci. 16:175)
Cholesterol oxides (ppm, dry wt. basis) in the
edible portions of commercial fish products
Sample
Lipid 7 β-OH 7-keto epoxides Triol 25-OH
Salt-dried
Anchovy
11.5
37.1
46.4
45.2
3.5
5.8
Northern cod
4.8
6.8
9.7
8.4
1.5
0.9
Jap. Whiting
6.8
24.5
24.9
25.0
3.4 10.7
Pacific herring 27.0
8.4
7.5
8.9
3.5
5.6
Boiled-dried
Anchovy
Shrimp
11.2
6.2
55.8
3.7
60.6
4.0
61.3
tr
8.5
tr
1.8
8.5
Smoked salmon
8.7
7.3
6.3
Ohshima et al. (1993, JAOCS 70:595)
5.7
2.7
4.8
Efforts to solve cholesterol problems
- Use of drug: bile salt sequestrants
(Cholestyramine), Nicotinic acid (decrease
VLDL production), HMGCoAR inhibitor
- Diet: increase n3 fatty acids and decrease
saturated fat consumption
- Removal of cholesterol from foods by
physical and chemical methods
Proposed Benefit of N-3 Fatty Acids
Omega-3 fatty acids reduce:
- Platelet aggregation
- Serum triglycerides
- Arterial spasm
- Blood pressure
- Serum cholesterol
Pathways for Eicosanoids Synthesis
Diet
Body
LTB4
LTC4
LTB5
LTC5
E,D
LA
LA
AA
L
AA
LNA
EPA
DHA
AA
E,D
E,D
LNA
EPA
EPA
DHA
DHA
AA
C
PGI2
TXA2
L
+
EPA, DHA
C
PGI3
TXA3
Mechanisms of action of EPA and DHA
L
C
LTB4, LTC4 <-------------- AA -----------------> PGI2, TXA2
L
C
LTB5, LTC5 <---------- EPA, DHA -----------> PGI3, TXA3
* LTB4, LTC4: increase adhesion of Leucocytes to endothelium
and inflammatory effects
* LTB5, LTC5: less effective than LTB4, LTC4
*PGI2: vasodilator, inhibit platelet aggregation
*PGI3: help effect of PGI2
*TXA2: increase platelets aggregation, vasoconstriction
*TXA3: less potent than TXA2
N3 fatty acids compete with N6 for elongase, desaturase,
cyclooxygenase and lipoxigenase
Possible adverse effects of high level
consumption of omega-3 fatty acids
- Depletion of tissue vitamin E
- Increased propensity to bleed
- Increased consumption of lipid oxidation
products
- Increased in vivo production of lipid
oxidation products
Effect of dietary fats on blood cholesterol
and the development of atherosclerosis in
rabbits
Fatty acid composition (%) and peroxide values of oils used
Item
Myristic acid
Palmitic acid
Palmitoleic acid
Oleic acid
Elaidic acid
Linoleic acid
Linolenic acid
Stearic acid
Eicosatetrenoic acid
Eicosapentanoic acid
Docosahexanoic acid
Other fatty acids
CO
FO
OO
HCO
----------- Fatty acid composition (%) --------------7.56
13.88
20.19
10.63
13.82
10.11
28.39
10.74
37.15
33.55
0.68
1.11
54.93
1.70
50.15
49.17
0.36
3.31
2.34
3.45
2.06
2.34
0.65
12.23
11.72
25.90
-
Peroxide value (PV)
--------------- meq peroxide/kg oil -------------------30.28
31.57
144.87
28.43
Abbreviations: CO, 2% fresh corn oil; FO, 2% fresh fish oil; OO, 2% oxidized oil; HCO, 2% heated corn
oil. Cholesterol (CHO, 1.5 g/kg diet)
Effect of various dietary oils on cholesterol
content in plasma
Dietary
treatment
NO
CO
FO
OO
HCO
Feeding periods (weeks)
0
3
6
9
12
------------------ cholesterol (mg/dL) ----------------------69.6
407.7
447.1
453.6
430.6
69.6
333.8
379.0
321.0
281.8
69.6
341.9
429.1
459.9
449.8
69.6
396.2
444.9
474.4
435.8
69.6
281.4
246.0
192.7
184.4
Abbreviations: NO, 0% oil; CO, 2% fresh corn oil; FO, 2% fresh fish oil; OO,
2% oxidized oil; HCO, 2% heated corn oil. Cholesterol (CHO, 1.5 g/kg diet) was
added to all the experimental diets.
Atherosclerotic lesions in aorta of rabbits fed
diets containing cholesterol and different oils
Dietary treatment 9 week
12 week
--------------- Score of lesions ------------------NO
2.25
3.75
CO
1.00
1.50
FO
2.25
2.75
OO
1.75
3.50
HCO
1.00
1.50
Abbreviations: NO, 0% oil; CO, 2% fresh corn oil; FO, 2% fresh
fish oil; OO, 2% oxidized oil; HCO, 2% heated corn oil.
Cholesterol (CHO, 1.5 g/kg diet) was added to all the
experimental diets.
Atherosclerotic lesions in aorta of rabbits fed
with different levels of dietary cholesterol
Results
„
No added oil and oxidized oil groups developed the highest
degree of atherosclerotic lesions followed by fresh fish oil, and
fresh corn oil and heated corn oil group had the lowest lesions.
„
Plasma total cholesterol level was the most critical factors
involved in the development atherogenic lesions in rabbit.
„
Dietary cholesterol and oxidation status of dietary lipids had
significant impact on lipid metabolism and the development of
atherosclerosis in rabbits.
„
Oxidized oils in diet accelerated the progress of atherosclerotic
lesions, but polymerization of oils by heating lowered plasma
cholesterol level and the development of atherogenic lesions in
rabbits by inhibiting the absorption of cholesterol in guts.